Underground fire is a kind of burning phenomenon which is difficult to control in the forest. It is very harmful to the forest. The temperature released by burning affects the spread of underground fire. Taking Larix gmelinii plantation in Daxing'anling area, one of the areas with frequent underground fire in China, as the research object, effects of humus particle size and combustion depth on the combustion temperature of underground fires were studied by the indoor control simulation of scorching experiment data. There were significant differences in the effects of different particle sizes and depths of humus on the maximum combustion temperature under different land classifications (P<0.05); there were significant differences in the effects of different land classifications, particle sizes of humus and their interaction on the maximum combustion temperature under different depths (P<0.05). Among five types of humus, the highest combustion temperature was at the particle size ≤ 80 mesh and the depth of 12 cm. The combustion temperature of underground fire was higher under the condition of tatoudianzi and meadow bog, especially in tatoudianzi. Depth, distance and humus particle size could be used as independent variables of the prediction model under the conditions of slope mountains, meadow bog and agricultural land, while depth and humus particle size could be used as independent variables of the prediction model under the conditions of tatoudianzi and flat mountains, and all the models passed the significance test (P<0.05). The results can provide scientific basis for the prevention and control of underground fire and the development of fire fighting equipment in this area.